Burner



BURNER Filed March 3, 1941 2 Sheets-Sheet l INVENTO FREDERICK DAL JOHNK. NORTHROP.

ATTORNEYS.

P 1942- F. DALLENBACH ET AL 2,296,023

BURNER Filed March 5, 1941 2 Sheets-Sheet 2 INVENTORS, FREDERICKDALLENBACH. QHN K. NORTHROP.

ATTORNEYS.

Patented Sept. 15, 1942 UNIT D STATES PATENT OFFICE BURNER FrederickDallenbach, Inglewood, and John K.

Northrop, Los Angelcs, Calif., assignors to Northrop Aircraft, Inc.,Hawthorne, Calif., a corporation of California Application March 3,1941, Serial No. 381,522

18 Claims.

This invention relates to burners and particularly to burners forproducing complete combustion of liquid or pulverized fuel in continuousflow gas turbines.

Among the objects of this invention are to provide a. burner which willpromote .the combustion of liquid or powdered fuel in a flow of airunder high compression and of relatively high velocity; to provide aburner which will produce maximum turbulence in the airstream withminimum air resistance consistent with the production of suchturbulence; to provide a burner wherein actual combustion takes place atvery high temperatures, and wherein, after combustion is complete, theproducts thereof are thoroughly mixed with large quantities of coolerair. to provide a uniform flow'of the mixed gases at a temperature whichis reduced .to the point where they may be employed in bladingconstructed of available materials; to provide a burner which is adaptedfor mounting in the turn of a reflexed air duct, without inducing undueresistance to flow in such duct; to provide a burner which is adapted tothe injection of water into the burned gases, thereby permitting the useof fuel in largerquantities than normal for the production of excesspower during short periods, such as the periods of takeoff of anairplane; to provide a burner having igniter means incorporated therein,and, generally, .to provide a burner giving high thermal andthermodynamic efllciency in gas turbines, particularly such as areadapted for aircraft use.

Our invention possesses numerous other objects and features ofadvantage, some of which, together with the foregoing, will be set forthin the following description of specific apparatus embodying andutilizing our novel method. It is therefore to be understood that ourmethod is applicable to other apparatus, and that we do not limitourselves, in any way, to the apparatus a of the present application, aswe may adopt vari-- ous other apparatus embodiments, utilizing themethod, within the scope of the appended claims.

Referring to the drawings:

Fig. 1 is an axial half section through the turbine unit and a portionof the compressor unit of a gas turbine embodying our invention.

Fig. 2 is a sectional view through the refiexed portion of the air ductsof the turbine of Fig. l, the plane of section being indicated by theline 22 of the first figure.

Fig. 3 is a partially schematic developed circumferential section of aburner of the general type shown in Figs. 1 and 2.

Fig. 4 is a schematic view similar to that of Fig. 3 showing a form ofthe burner as modified to give a longer combustion chamber.

In turbines of the type contemplated by the present invention, air iscompressed adiabatically to a relatively high pressure, e. g., apressure of the order of six and a half atmospheres, fuel oil isinjected into the compressed air stream and there burned to add thermalenergy to its flow, and the products of combustion are expanded inturbine blading to provide the energy necessary to precompress the airplus excess useful power. The maximum temperatures thus produced, ifcombustion is to be complete and high efiiciency thereby obtained, aregreatly in excess of those which can be borne by materials available atthe present time. a In order to reduce such temperatures to reasonablelimits, large quantities of excess air are provided. It is highlydesirable that the excess air be thoroughly mixed with direct productsof combustion, and to accomplish such mixing the flow in the mixingregion should be highly turbulent. Turbulence also promotes thecompletion of combustion itself due to the mixing action of the fuel oiland air particles, as does the fact that combustion takes place underhigh pressure. Turbulence after combustion produces a more uniformdistribution of temperature throughout the combustion chamber in ashorter time as a result of the increased convection of heat.

. Considered broadly our invention comprises a nozzle mounted in theduct and directed in the general direction of flow to produce a jet orspray of oil traveling with the flow. Placed adjacent to the dischargeof the nozzle is a pair of vanes preferably mounted symmetrically withrespect to the axis of the nozzle and diverging from the leading to thetrailing edges of the pair to produce a "stalled condition. Preferablythe nozzle is supported by a streamlined body, having the generalcharacteristics of an airfoil mounted in neutral relation to the flowand with the nozzle dischargingfrom its trailing edge. The divergentvanes are also preferably of airfoil section, since such sectionproduces minimum obstruction to a flow even though the airfoil bestalled. Where relatively large quantities of fuel are to be consumedadditional vanes may be supplied, also preferably of airfoil section,and mounted generally parallel to the axis of the nozzle, thus forming asubsidiary passage with the nozzle directed into its entrance and thedivergent vanes adjacent its outlet. The nozzle should produce adivergent spray, and igniter means may be incorporated in the faces ofthe vanes where this spray impinges upon them, and, for cases whereoverload capacity is to be provided by the addition of water vapor, thedivergent vanes are provided with water passages and Jets in theirproximal surfaces, whereby steam is produced in .the portion of the airflow which is at maximum temperature and which has maximum turbulence.

Even a perfectly flat and unstreamlined plate will exhibit thecharacteristics mentioned in some degree. The values of lift and dragwill, however, be very different betwen a true airfoil section and afiat plate, and at the minimum angles at which complete or nearlycomplete stalling occurs the drag on an airfoil section will bematerially less than that on a flat plate, although, when fully stalled,they will produce equal turbulence.

In our invention the turbulence produced by the stall is utilized to mixthe combustion products with the relatively cool pure air. The burnerordinarily comprises a plurality of units, each consisting of nozzle anddivergent vanes. Preferably the spacing of the units is considerablygreater than the spacing between the vanes comprising each pair. Theflow between the units is smooth until it passes the trailing edges ofthe stalled vanes, but at this point there is a sudden discontinuity offlow, inducing a turbulence which augments and is, in fact, a part ofthe turbulence induced between the vanes of the pair. The turbulencecauses a pressure drop which represents a loss of energy,.but this lossis a minimum with vanes of airfoil section and hence it is desirablethat all of the vanes be made of such section, even though the devicewould be operative were flat plates used instead.

Fig. 1 of the drawings shows a portion of a turbine embodying thisinvention. At the right hand side of the drawing is shown a finalcentrifugal stage I of the compressor unit of the turbine, this stagenot being shown completely as it does not relate directly to the presentinvention and is completely described in the copending applications ofPavlecka and Northrop, Serial No. 403,338, filed July 21, 1941, and ofPavlecka, Serial No. 385,105, filed March 25, 1941.

The centrifugal rotor I discharges through diffuser 2 and thence into anannular duct '3 formed within a cylindrical outer casing 4 of theturbine. The duct 3 discharges into a substantially semitoroidal endcasing 5 which forms a reflexing turn of the duct. The casing 5 isprovided at uniformly spaced intervals with spoke-like vanes 'I whichsupport an inner annular core 9. The core 9 serves as an abutment ormounting for a tubular barrier having double walls I and I I, the wallI0 forming the inner wall of the duct 3 and the wall II forming theouter wall of an annular duct 3' which forms a continuation of the outerduct beyond the refiexing turn. The inner wall of the duct 3 is formedby a conical casing I2, supported on a frame I3 which carries the statorblading I4 of the turbine. A rotor I of the turbine carrying blading I'Irotates within this frame on bearings I9, but since the turbinestructure proper is not involved in the present invention it will nothere be described in detail.

The spoke-likevanes 1 are formed of streamlined or airfoil section,mounted neutrally with respect to the flow of the air stream induced bythe compressor unit. In order to guide the flow around the reflexingturn there are provided a plurality of guide vanes 20, annular in thedirection of span, and supported on the vanes 'I.

The vanes 1 also carry burner nozzles 2|, which terminate in fittings 22which enter through the end casing 5. The trailing edges of the vanes Iare notched as is shown at 23, and the nozzles, supplied with oil underpressure through the pipes 24, discharge a conical or pyramidal spray ofil in the direction of flow of the air in the duct.

Disposed on either side of the axis of the nozzle is a pair of vanes 25,only one of which is shown in Fig. 1. The shape and disposition of thesevanes can more clearly be seen from Fig. 3, which is a simplifieddevelopment of a similar arrangement. In this latter figure thestreamlined vane I in the toroidal passage has been replaced by anequivalent but shorter vane I carrying a. nozzle 2|. With this exceptionthe diagrammatic representation of Fig. 3 may be taken as though it werea circumferential section taken on the mean radius of the duct 3', thevanes 25 occupying the same relative position with respect to thedischarge of the nozzle 2| as the vanes 25 occupy .with respect to thenozzle 2 I.

As has been indicated in the general discussion, above vanes 25' are ofairfoil section, mounted at an angle with respect to the airflow, whichangle is equal to the angle of complete or nearly complete stall forsuch vanes in a medium of the density of the compressed air in whichthey are to work.

In the diagram there is shown, 'gsomewhat roughly, the effect of thevanes, thus mounted, on the airflow. Considering the vanes as thoughthey were airplane wings, the fiow along the lower or distal surfaces issubstantially laminar or streamlined up to the trailing edge of theairfoils. On the upper or proximal surfaces of the airfoils, however,the streamlined flow breaks away from the surface, causing a high degreeof turbulence in the flow for the latter two-thirds or more of thesurfaces of the airfoils. Considered in the direction of flow,therefore, the greater part of the space between the proximal surfacesof the pair f vanes is turbulent, and this turbulence extends past thetrailing edges and is increased by the xpansion of the airflow from thedistal surfaces as the flow between adjacent pairs passes the trailingedges of the wings. A short distance beyond the ends of the vanes,therefore, the entire flow becomes turbulent, resulting in a verycomplete mixture of the burned gases with the relatively cool air fromboth adjacent pairs of vanes.

Built in means are provided for igniting the fuel. Embedded in thesurface of each of the vanes 25 is a resistance type heater or glow'rod21. A similar igniter element is shown in Fig. 3, being indicated by thereference character 21'. At the time of starting the burning theseelements can be raised to incandescence by current supplied through leadwires carried in the channels 29. One end of the igniter element can begrounded to the vane and a single wire connected to the other end,insulated with refractory insulation such as is used in high temperatureelectric furnaces, the particular material and character of the igniterelements not being considered a portion of this invention, since suchelements are known in the art, but their positioning within the vanes isso considered. Water may be supplied to the turbulent flow throughconduit 28' in the stalled divergent vanes 25'.

Fuel spraying nozzles of the type used in this, as in most otherburners, project a divergent the discharge of the nozzle.

of the operation of the burner, since once ignition has taken place thevanes arerapidly raised to a temperature which is of itself sufficientto cause ignitiomand the flame, moreover, is selfsustaining,

In the particular turbine shown in Fig. 1, ow-' to the impulse buckets32 of an inwardly-radialflow turbine stage.

The gases are then redirected axially by a guidevane 33 to a set ofexpansion nozzles 34, which are of the impulse type although they rotateas a unit with the impulse buckets 32. Nozzles 34 in turn discharge intoreaction type stator blades 35. Nozzles 3| and buckets 32 thus form whatmay be considered as an impulse stage which feeds an inverted impulse or(theoretically) 100 per cent reactionstage constituted by the nozzles 34and blades 35. The gases are greatly cooled by their expansion throughthese two stages and thence fed into the more conventional reactionblading l4 and I! already described and so to the exhaust 31.

Although in the present turbine complete combustion can occur in therelatively short distance represented by the length of the vanes 25,there are conditions where, because of different pressures, amounts offuel to be consumed, or different quantity of secondary air, it isdesirable to provide additional combustion space before completeturbulence is induced, and this can be accomplished by modifying theburner as is shown in Fig. 4. r

This modification involves the use of an additional set of vanes 40,mounted on either side of the nozzle axis. The vanes 40 are mountedgenerally parallel to the axis of the nozzle, and are preferably ofairfoil section for reasons which have already been discussed. Thenozzle 2|" projects well into space between the vanes 40 from thedirection of their leading edges, and the camber of these vanes acts tosome degree as a venturi, speeding the flow of the air past In this casethe igniters 21" are mounted in the faces of the parallel vanes, withinthe range of the spray cone, instead of in the surfaces of the divergentvanes. The latter are mounted with their leading edges projectingslightly into the discharge end of the subsidiary passage formed by theparallel vanes 40.

A portion of the burned gases will pass between the stalled divergentvanes 25", and be set into turbulence as in the case where these vanesare mounted immediately adjacent the nozzle, A further portion of thecombustion products will pass without the divergent vanes, over theirdistal surfaces, but this latter portion will in general follow astreamline flow until it has reached the trailing edges of the divergentvanes, after which it is thoroughly mixed with the unburned air. Inother words, it is not necessary to the action of the burner that all rof the burned gases pass between the vanes,

and that all of the air that passes on the outer side of the vane berelatively cold. The important point'is that sufficient turbulence beset up, to mix the burned gases and the secondary air completely beforethe mixed gas reaches the first turbine stage, and this is accomplishedby the stalled vanes.

It is obvious that the water spray can be produced in the modificationof the burner shown in Fig. 4 in the same manner as in the simpler form.

We claim:

1. A bumer' comprising a substantially unobstructed duct and means forcausing an air flow therethrough in a substantially constant generaldirection, a nozzle for injecting a spray of fuel into said airflow inits general direction of motion and a vane positioned on each side ofsaid airflow, said vanes having facing surfaces positioned on each sideof said airflow at a substantially critical aerodynamic stalling angleof attack thereto, to produce turbulence in said airflow between saidsurfaces without substantial baffling thereof.

2. A burner in accordance with claim 1 wherein said vanes are of airfoilsection.

3. A burner comprising a duct for carrying compressed air, a fuel nozzlepositioned in said duct and directed in the general direction of airflow therein, and a pair of vanes positioned beyond said nozzle in thedirection of said flow,

said vanes diverging symmetrically from the axis of discharge of saidnozzle to produce a stalled condition with relation to said flow.

4. A burner in accordance with claim 3 wherein said vanes are of airfoilsection.

5. A burner in accordance with claim 3 comprising a plurality of saidnozzles and vanes, the spacing between adjacent pairs of vanes beingrelatively large in comparison with the spacing between the vanes ofeach pair.

6. A burner comprising a compressed air duct, 2. pair of vanes forming asubsidiary passage within a portion of said duct, a fuel nozzle adaptedto produce a divergent spray and discharging into one end of saidpassage and in the general direction of air flow in said duct, andigniter means for said fuel spray embedded in said vanes within therange of said spray.

7. A burner comprising a compressed air duct, a pair of substantiallyparallel vanes form- 'ing a subsidiary passage within said duct, a fuelnozzle discharging into the inlet end of said passage, and a second pairof vanes positioned with their leading edges adjacent the discharge endof said passage, said second vanes diverging to produce a stalledcondition thereof with respect to air flow in said passage.

8. A burner in accordance with claim 3 including means for discharging ajet of water from the proximal faces of at least one of said divergentvanes.

9. A burner comprising an air duct, a streamlined vane positioned inneutral relation to air flow in said duct, a fuel nozzle mounted on saidvane to discharge from the trailing edge thereof, and a pair of vanespositioned beyond said nozzle in the direction of said flow, said vanesdiverging symmetrically from the axis of discharge of said nozzle toproduce a stalled condition with relation to said flow.

10. A burner comprising an air duct reflexed within itself to form twocoaxial annular passages, a plurality of vanes positioned at thereflexing turn of said duct, and supporting the division between saidannular passages, fuel nozzles mounted in said vanes to dischargesubstantially at the trailing edges thereof, and a pair of vanespositioned beyond each of said nozzles in the direction of flow withinsaid duct, said last mentioned vanes diverging symmetrically from theaxes of discharge of said nozzles to produce a stalled condition withrespect to said flow.

11. A burner in accordance with claim wherein each of said vanes is ofstreamlined section.

12. A burner in accordance with claim 10 wherein the direction of flowis from the outer to the inner of said coaxial annular passages.

13. A burner in accordance with claim 10 including an annular guide vanefor directing flow around said reflexing turn, said guide vane beingsupported upon said nozzle mounting vanes.

14. A burner in accordance with claim 3 wherein said duct is annular andwherein a plurality of said nozzles and vanes are equally spaced in saidduct, the spacing between adjacent pairs of vanes being relatively largein comparison with the spacing between the vanes of each pair.

15. A burner in accordance with claim 3 wherein said duct is annular andwherein a plurality of said nozzles and vanes are equally spaced in saidduct, the spacing between adjacent pairs of vanes being relatively largein comparison with the spacing between the vanes of each pair, andwherein said vanes are of airfoil section.

I compressed air, a fuel nozzle positioned in said duct and directed inthe general direction of air flow therein, a member positioned on eachside of and beyond said nozzle in the direction of said flow, saidmembers having facing surfaces of airfoil profile disposed at an angleto said flow creating a stalling turbulence therein as said flow passesbetween said surfaces.

18. A burner structure comprising a substantially unobstructed ducttherein for carrying an airflow in -a substantially constant generaldirection, a fuel nozzle positioned at the entrance of said duct anddirected in the general direction of said airflow, and facing surfacesforming opposite walls of said duct beyond said nozzle, said surfacesbeing shaped to present a substantially critical aerodynamic stallingangle of attack to said airflow to create turbulence in the airflowthrough said duct with out substantial bailling thereof.

FREDERICK DALLENBACH. JOHN K. NOR'I'HROP.

